Method and forming machine for manufacturing a product having various diameters

ABSTRACT

The invention relates to a method and a forming machine suitable for manufacturing a product having various diameters from a workpiece, such as a metal cylinder or plate, in which the workpiece is clamped down in a clamping device, the workpiece and a first tool are rotated about an axis of rotation relative to each other, the workpiece is deformed by means of said first tool by placing the tool into contact with the workpiece and moving the workpiece and/or the tool in a direction along the axis of rotation. At least a second tool is placed into contact with the workpiece at a position behind the first tool, seen in the working direction, and the workpiece is also deformed by means of said second tool. Thus, parts of the workpiece that have been deformed by the first tool are deformed by one or more subsequent tools practically immediately.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application ofInternational Application No. PCT/NL03/00030, filed Jan. 17, 2003 andpublished as WO 03/059547 on Jul. 24, 2003, in English.

BACKGROUND OF THE INVENTION

The invention relates to a method and a forming machine suitable formanufacturing a product having various diameters from a workpiece, suchas a metal cylinder or plate, in which the workpiece is clamped down ina clamping device, the workpiece and a first tool are rotated about anaxis of rotation relative to each other, the workpiece is deformed bymeans of said first tool by placing the tool into contact with theworkpiece and moving the workpiece and/or the tool in a direction along,i.e. parallel to or having a component parallel to, the axis ofrotation.

Such a method and apparatus are known, e.g. from EP 0 916 426. Saidpublication describes how one end of a cylindrical workpiece is workedby clamping down said workpiece in a clamping device (indicated bynumeral 12 in FIG. 1 of EP 0 916 426) and deforming said ends by meansof three forming rollers (28), which are mounted on a rotary member(24). Said forming rollers (28) rotate in the same plane and are pressedagainst the workpiece at three locations which are evenly distributedover the circumference of the workpiece, after which said rollers movealong a number of paths along the workpiece so as to deform theworkpiece in steps.

For the sake of completeness, attention is drawn to DE 23 27 664 and DE1964 401, in which methods and apparatuses are described for flowpressing cylindrical tubes, i.e. tubes having a constant diameter. Themethods and apparatuses according to these documents are unsuitable formanufacturing a product having various diameters. JP 2000301246 alsorelates to a method and apparatus for flow pressing cylindrical tubes.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved method and formingmachine.

In order to accomplish that objective, the method and the formingmachine referred to in the first paragraph are characterized inaccordance with the independent claims.

Preferably, the tools each comprise two or more forming rollers, betweenwhich the workpiece is retained while being worked and which occupysubstantially the same axial position with respect to the workpiece. Itis possible to impose relatively large as well as relatively smalldiameter changes by means of forming rollers. Such rollers arepreferably freely rotatable about an axis, which extends eitherhorizontally or at an angle with respect to the aforesaid axis ofrotation. Furthermore, it is preferred that most or all of the toolsform part of one and the same deforming head, or that they are at anyrate positioned relatively close together. The question as to the mostsuitable spacing between successive tools, at least between thepositions at which the tools make contact with the workpiece, depends onthe properties of the workpiece, of course, and on the nature of theworking process to be carried out. In many cases said spacing will varybetween 1 and 30 cm.

If the material and the dimensions of the workpiece and the intendedproduct (frequently a semifinished product) allow so, the number ofworking cycles can be reduced to one, if desired. A surface that hasbeen worked once will not be worked anew in that case, so that the loadto which the material is subjected will remain limited. In addition tothat the programming of any control equipment that may be provided willbe significantly simpler, in particular because it will not be necessaryto take the shape and the behaviour of various intermediate forms intoaccount.

For the sake of completeness it is noted that British patent applicationNo. 238,960 describes a roller by means of which the diameter of bars,pipes and the like is reduced to a smaller, uniform diameter in acontinuous process, using a number of tools arranged in succession.

Further, attention is drawn to U.S. Pat. No. 5,428,980, in which aworkpiece is deformed with a first forming roller and glazed with asecond roller. A second forming roller is not described.

JP 59 193724 relates to a device wherein plural rollers having differentshapes have been attached to a tool rest. The rollers are disposed “in away as not interfere with the respective parts of the device and a blankmaterial during working”.

The invention will be explained hereinafter with reference to thefigures, which show a number of embodiments of the method and theforming machine according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically show the deformation of one end of acylindrical workpiece by means of five tools.

FIGS. 2A and 2B show the eccentric deformation of one end of a workpieceby means of three tools.

FIGS. 3A-3C show the fixing of an insert member in a cylindricalworkpiece, using a method comparable to the method as used in FIGS. 2Aand 2B.

FIG. 4 is a cross-sectional view of a forming machine for eccentricdeformation of a workpiece, which machine comprises four tools.

FIGS. 5A and 5B are front views of a workpiece which has been subjectedto one operation and two operations, respectively, by means of theforming machine of FIG. 4.

FIG. 6 is a top plan view of a forming machine which is in particularsuitable for deforming relatively long workpieces.

FIGS. 7 and 8 are a front view and a perspective view, respectively, ofa so-called carriage for use in a forming machine as shown in FIG. 6.

FIGS. 9A and 9B are schematic sectional views of the carriage of FIGS.6-8.

FIG. 10 shows the flow forming process carried out by using the presentinvention.

FIG. 11 shows the so-called bottom-closing process carried out by usingthe present invention.

FIGS. 12A-12D schematically show the rotary deep drawing of aplate-shaped body carried out by means of seven tools.

FIGS. 13A-13D schematically show the projection of a plate-shaped bodyby means of six tools.

FIGS. 14A-14D schematically show a variant of the projection process ascarried out in FIGS. 13A-13D.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Parts which are identical or which have the same or substantially thesame function will be indicated by the same numerals as much as possiblehereinafter.

FIGS. 1A and 1B schematically show a method and apparatus according tothe present invention. A workpiece 1, in this case a metal cylinder, isrotated about an axis of rotation 2 at a certain number of revolutions.Subsequently a deforming head (not shown) is provided, in which fivetools 3A-3E are rotatably mounted. Each tool 3 comprises two formingrollers arranged in mirror symmetry with respect to the axis 2. Theradial distance from the tools 3 to the axis 2 decreases stepwisetowards the rear, seen in the working direction 4 such that perimetersP1, P2 of adjacent forming rollers at least partially overlap.

FIG. 1A shows the start of the operation, in which the first formingrollers 3A just make contact with the edge of an end of the rotatingworkpiece 1, whilst FIG. 1B shows the situation after one working cycle,in which the forming rollers 3 have made a full pass in the workingdirection 4, having deformed the workpiece 1 into a product having fivegradually decreasing (in steps) diameters. The part having the smallestdiameter has been deformed on a mandrel 5 by the final forming rollers3A, so that the inside diameter of said part is precisely calibrated.

The magnitude of the steps by which each tool 3 is positioned closer tothe axis of rotation 2 than the preceding tool inter alia depends on thedesign, the material and the dimensions of the unformed workpiece, ofcourse. In the case of a workpiece having a small wall thickness, itwill usually be possible to use larger steps.

FIGS. 2A and 2B show a second embodiment of the present invention, inwhich the tools 3A-3C, likewise comprising two forming rollers each inthis embodiment, are freely rotatable in holders 6A-6C. The holders 6are in turn rotatably mounted, about an axis of rotation 2, in adeforming head 7 (schematically shown). Also in this embodiment theradial distance from the tools 3 to the axis 2 decreases in stepstowards the rear. The holders 6 can be adjusted independently of eachother in radial direction. This makes it possible to position saidholders 6, and thus the axis of rotation 2 of each of the tools 3,eccentrically with respect to the central axis 8 of the (undeformed asyet) workpiece 1.

By rotating the holders 6 and moving the deforming head 7 in the workingdirection 4, using driving means 9 (schematically shown) such as apneumatic or hydraulic cylinder or an electric motor fitted with aspindle, over a workpiece 1 clamped down in a fixed clamping head 10(schematically shown), said workpiece 1 is deformed in one singleoperation, in which the worked parts obtained are positionedeccentrically with respect to the axis 2.

For the sake of completeness it is noted that the frictional heat whichis generated during the deforming operation can be influenced bydisposing the forming rollers at an angle with respect to the axis ofrotation 2. In the case of an inclined position (FIG. 2A) lessfrictional heat will be generated than in the case of a position atright angles (FIG. 2B). This position may be varied in dependence on theheat that is required with a particular operation.

FIGS. 3A-3C show how parts can be fixed in a workpiece by means of theforming machine as shown in FIG. 2B, e.g. in order for the purpose ofmanufacturing a catalytic converter for a passenger car.

First a so-called catalytic brick or substrate 11A and an insert member11B are placed in the workpiece 1 (FIGS. 3A and 3B). The insert member11B may be supported and placed by means of, for example, an axiallyadjustable mandrel (not shown) mounted in or through the deforming head7. Following that, the workpiece 1 is deformed by a deforming head 7, inwhich the end of the workpiece 1 is pressed onto the end of the insertmember 111B and in which a substantially gastight connection between thetwo ends is obtained.

FIG. 4 is a cross-sectional view of a second forming machine foreccentric deformation of a workpiece, which machine comprises four tools3A-3D. Each tool 3 comprises minimally one forming roller, which is(are) mounted freely rotatable on a separate holder 6A-6D. The holders 6are arranged in pairs, opposite each other, in four separaterotationally symmetrical housings 12A-12D, which housings in turn formpart of a deforming head 7. The first housing 12A comprises asubstantially annular, static outer part 13A, in which a, likewisesubstantially annular, inner part 14A is rotatably mounted in bearings15A. The inner part 14A may e.g. be driven by means of a motor 16A(schematically shown), whose drive shaft is fitted with a pinion 17A,which engages in a set of teeth present on the circumference of theinner part 14A. In addition, an annular element 18A of wedge-shapedsection, which element 18A mates with an end 19A, likewise ofwedge-shaped section, of the respective holder 6A, is present in saidinner part 14A. By moving the annular element 18A to the left or theright (in the drawing), using driving means 20A, the holders 6A, andthus the forming rollers mounted thereon, are moved radially inwardly oroutwardly, respectively. Furthermore, driving means 21A are provided, bymeans of which the housing 12A can be adjusted in axial direction,parallel to the axis of rotation 2, with respect to the other housings12.

The other three housings 12B-12D correspond to a large extent to thefirst housing 12A, but in addition they comprise a circular cylindricalpart 22, whose outside diameter is smaller than the inside diameter ofthe housing 12 to the left (in the drawing) thereof. As a result, thehousings 12 can also be adjusted in radial direction relative to eachother, independently of each other, by means of respective drivingmechanisms 23A-23D, and the axis of rotation 2 of each of the housings12 can be positioned eccentrically relative to the central axis of (thepart as yet undeformed of) a workpiece.

The annular elements 18B-18D in turn each comprise a cylindrical part24, whose outside diameter is smaller than the inside diameter of theinner part 14B-14D. Furthermore, the deforming head 7 comprises drivingmeans 9, by means of which said head 7 can be moved forward and backwardin the working direction. Examples of the aforesaid driving means 9, 20,21 and 23 include a pneumatic or hydraulic cylinder or an electric motorfitted with a spindle. The driving means are not limited to the aboveexamples, of course.

FIGS. 5A and 5B are front views of a workpiece 1 which has been deformedinto an (intermediate) product 25 comprising four reduced portions inone working cycle. By subsequently adjusting the tools 3 in outwarddirection, the (intermediate) product 3 can be deformed into a product25 comprising a total of eight reduced portions in a working cycle, inwhich the stroke is extended by half the axial distance between thefirst reduced portions. It stands to reason that it is possible to adaptinter alia the number of tools 3, the number of working cycles and thedegree to which the tools are adjusted to the required product. ThusFIG. 4 shows a working process in which the tools are adjusted duringthe working cycle(s), so that a product having a continuously decreasingdiameter, in this case a product having a conical end, is obtained.

FIG. 6 is a top plan view of a forming machine by means of which alsorelatively long cylindrical workpieces 1 can be deformed. The formingmachine comprises a frame 30, which is provided with guide rails 31, 32on either side, on which a transversely arranged subframe 33 issupported, over which guide rails three so-called carriages can bemoved.

The subframe 33 comprises a clamping head 34, in which a first end of aworkpiece 1 can be clamped down and which can be rotated, e.g. by amotor which is accommodated in a housing 35.

The first carriage 36 is provided with a carrier plate 37, on which fourtools 3 are mounted. Each tool comprises two forming rollers, which aremounted freely rotatable in holders 38 positioned directly opposite eachother. Said holders 38 are in turn tiltably mounted, about respectivetilting points 39, on radially adjustable supports or slides 40 and theycan be tilted in a direction towards the axis of rotation 2 and in adirection away therefrom, using driving means such as electric motors 41or hydraulic cylinders, which are likewise mounted on respective slides40. The slides 40, and thus the holders 38 and the forming rollers, canbe adjusted in radial direction, using driving means 9. In theillustrated embodiment, the slides 40 are moreover detachably connectedto the carrier plate 37, so that the number of slides 40, the number oftools 3 and the positions thereof can easily be adapted to the productto be manufactured. In the illustrated embodiment, the tilting points 39are located behind the tools 3, seen in the working direction, but saidtilting points 39 may also be located at other positions, e.g. in frontof or between the tools 3, depending on the operation, or they may evenbe adjustable. In the latter case the tilting points can be shiftedduring operation.

The second carriage 42 comprises a passage 43, in which a centeringunit, e.g. a bush (not shown), is present, whose central axis coincideswith the axis of rotation 2 and which functions to centre a workpiecepresent therein with respect to said axis 2. The third carriage 44comprises a so-called tailstock 45, which supports the other end of theworkpiece 1 during the operation and which comprises a mandrel 5 orclamping mandrel. Depending on the operation, the second and/or thethird carriage can be coupled to the first carriage, e.g. if it isdesirable to maintain a substantially constant distance between thefirst and the second carriage.

A cylindrical workpiece 1 can be loaded into the forming machine, e.g.by moving the third carriage 44 to the front (to the left in the figure)and moving the first and second carriages 36, 42 to the rear until thedistance between the third carriage 44 and the second carriage 42 isgreater than the length of the workpiece 1. Then the workpiece 1 isguided through the passage 43 and between the tools 3 with its first endand clamped down in the clamping head 34. The mandrel 5 is placed in thesecond end of the workpiece 1, after which the workpiece 1 is centred,the tools 3 are set and the mandrel 5 is placed into contact with thewall of the workpiece 1. It is also possible to remove the workedworkpiece 1 automatically, e.g. by means of a pick and place system,after an operation, when all three carriages are positioned on the left,and load a next workpiece into the machine in the same position of thecarriages.

The outside diameter of the workpiece 1 can be reduced to a smaller,constant outside diameter, e.g. along the full length of the workpiece,by rotating the workpiece 1 about the axis of rotation 2, graduallytilting the tools 3 and moving the slides 40 in radial direction towardsthe workpiece 1 and initiating a translating movement of the carriages.The rear tool 3D will be the first to make contact with the workpiece 1,followed by the third, the second and the first tool, respectively. Itis also possible to have 3D and 3C, or even all the tools 3, makecontact with the workpiece at the same time. The so-called “escaping” ofthe material can be suppressed more easily in this way.

Preferably, the end of the mandrel 5 is only spaced from the front tool3 by a small distance at all times, at any rate towards the end of aworking operation, in order to support the workpiece 1 up to a pointjust before the working zone and thus further enhance the degree ofstability. In addition, the mandrel 5 can be used for generating atensile force in the workpiece 1. Such a tensile force can be used foradjusting the reduction of the wall thickness along the entire length,or practically the entire length, of the product or in particular zonesthereof. As the force exerted on the workpiece by means of the mandrel 5increases, the rate at which the material of the workpiece 1 is pulledfrom the mandrel 5 will decrease, which will in turn result in a smallerwall thickness. It is noted that the tensile force in the workpiece canbe varied by means of the aforesaid centering unit in the passage 43 aswell. Thus the tensile force can be imposed at the start of the workingprocess, for example, in particular by means of said centering unit,whilst the tensile force can be imposed mainly by the mandrel 5 towardsthe end, when the workpiece 1 starts to exit from the bush.

Incidentally, wall thickness and wall thickness variations can becontrolled by varying the radial distance between consecutive tools, forinstance by tilting the holders and translating the holders in radialdirection, preferably simultaneously. By increasing or decreasing theradial distance between the tools, the wall thickness at that locationwill be reduced or increased respectively.

FIGS. 7 and 8 show variants of the first carriage 36, in which thecarriage is shown to be fitted with, respectively, two and six tools.

FIGS. 9A and 9B show the manner in which the tools 3 can be tiltedtowards the workpiece in carriages as shown in FIGS. 7 and 8 and, afterthe tools have started their working stroke, be moved in radialdirection towards the definitive working position. Using the apparatusas shown in FIGS. 6-9B, a tapered and/or stepped product can beobtained, for example, by adjusting the tools 3 during operation. It isalso possible to form two or more products from a workpiece andsubsequently separate said products from each other.

The number of revolutions, the magnitude of the steps and the rate oftranslation of the tools depend on factors such as the material beingused, the outside diameter and the wall thickness of the workpiece andthe dimensions of the intended product. An aluminium tube having adiameter of 25 cm and a length of 4 m, for example, can e.g. be formedinto a conical tube having a diameter which decreases from 16 cm to 8 cmand a length of 7 m. Such an operation can usually be carried out at arotational speed of 200-700 revolutions per minute.

FIG. 10 shows an embodiment in which a cylindrical workpiece 1 is placedonto a mandrel 5 until the closed bottom of said workpiece 1 abutsagainst the end of the mandrel 5, which workpiece is clamped down bymeans of a tailstock (not shown) and deformed by means of a flow turningoperation. This makes it possible to control the surface quality of theinner wall and, more in particular, prevent porosity of said inner wall.In addition to that it is possible to manufacture a finished producthaving a variable wall thickness in a single working cycle by adjustingthe tools in radial direction during operation.

FIG. 11 shows how the invention can be used for a process that is alsoreferred to as “bottom closing”. In this process, the open end of acylindrical workpiece 1 is closed in one operation, using a number oftools 3 which are each mounted on their own slide, and which can thus bemoved relative to each other. Said adjustable slides are in turn mountedon a support (not shown), which can be pivoted about an adjustable pivotpoint 39, using driving means as already mentioned before. Since therespective operations of the tools are carried out in quick succession,the risk of adverse effects caused by premature cooling is considerablyreduced or even practically eliminated.

FIGS. 12A-12D show an example of the rotary deep-drawing of aplate-shaped workpiece 1, in this case a metal disc, in which saidworkpiece 1 is pressed against the central part of a bobbin 46 by meansof a tailstock (not shown) and is rotated together with the aforesaidparts. The workpiece is deformed by means of five tools 3, which eachcomprise a number of forming rollers. Said forming rollers are eachmounted on a separate slide (not shown), so that the rollers can bemoved relative to each other during the deforming process. The edge ofthe workpiece 1 is stabilised by a support or holding-down clamp 47, atleast during the initial part of the operation. In the illustratedexample, the final tool 3E can directly move along a path correspondingto the outside diameter of the intended product, because the other tools3A-3D have sufficiently pre-formed the workpiece 1.

FIGS. 13A-14D show examples of the so-called projecting of aplate-shaped workpiece 1, likewise a metal disc in this case, which ispressed against a bobbin 46, by means of a tailstock (not shown), androtated. The workpiece is deformed by means of seven tools 3, viz. sixdiscs 3A-3F and one forming roller 3G, which are mounted on a commontiltable slide. The discs mainly function to pre-form the edge of theworkpiece relative to the block 46, whilst the forming roller projectsthe material by means of a flow turning operation. FIGS. 14A-14D showhow the forming roller on the one hand and the six discs on the otherhand are mounted on either side of the block 46, each on a separateholder 47, 48, which holders can be moved in the X-direction and theY-direction by means of two respective slides. For more details withregard to the projection process, reference is made to EP 0 774 308.

If the workpieces are deformed in only one working cycle in the formingmachines as described above, the tools, the centering means and the likewill require no readjustment, and in many cases less residual material,e.g. an undeformed end which was fixed in a loose chuck, or even noresidual material at all will remain.

The forming machines according to the present invention can be operatedby a person as well as by a control unit, of course. Such a control unitwill be arranged, for example, for controlling the movement of the toolsand the workpiece relative to each other, e.g. in axial and radialdirection or along X- and Y-coordinates, in accordance with a controlprogramme stored in a memory, in such a manner that the tools will movealong one or more desired paths for forming the workpiece into thedesired finished product or intermediate product.

Although the invention has been explained on the basis of a circularcylindrical metal workpiece in the foregoing, the invention can also beused with workpieces of unround section(s), such as oval, substantiallytriangular or multilobal sections. The invention can furthermore be usedfor hot forming as well as for cold forming.

The term “tool” as used within the framework of the present inventioninter alia comprises a single forming roller and sets of two or moresuch forming rollers, which take up substantially the same axialposition with respect to the workpiece.

Consequently, the invention is not restricted to the embodiments asdescribed above, which can be varied in many ways within the scope ofthe invention as defined in the claims.

The invention claimed is:
 1. A method for manufacturing a product havinga constant diameter or various diameters from a workpiece, in which theworkpiece is clamped down in a clamping device, the workpiece and afirst set of forming rollers are rotated about an axis of rotationrelative to each other, wherein the rollers of the first set take up afirst same axial position with respect to the work piece, wherein theworkpiece is deformed by means of said forming rollers by placing theforming rollers into contact with the workpiece and moving the workpieceand/or the forming rollers in a direction along said axis of rotation,wherein at least a second set of forming rollers positioned at a secondsame axial position with respect to the work piece is placed intocontact with the workpiece at a position behind the first set of formingrollers, the workpiece also being deformed by means of said second setof forming rollers and wherein two or more forming rollers, each beingof a different set and taking up a different axial position with respectto the work piece, are mounted on a common holder and said holder istiltable about a tilting axis toward and away to said axis of rotationwherein said tilting axis crosses said axis of rotation during theworking of the workpiece into a selected shape.
 2. The method accordingto claim 1, wherein at least a third set of forming rollers are placedinto contact with the workpiece at a position behind the second set offorming rollers.
 3. The method according to claim 1, wherein the firstand second set of forming rollers each comprise two or more formingrollers, between which the workpiece is retained while being worked. 4.The method according to claim 1, wherein the workpiece is formed into afinished or semifinished product in only one working cycle.
 5. Themethod according to claim 1, wherein a tensile force is exerted on theworkpiece.
 6. The method according to claim 5, wherein said tensileforce is varied during said working.
 7. The method according to claim 1,wherein at least one of the first or second set of forming rollers isadjusted in a radial direction during said working.
 8. The methodaccording to claim 1, wherein the workpiece has an open end, which endis closed by means of the forming rollers.
 9. The method according toclaim 1, wherein the workpiece is a plate-shaped body, and wherein thecentral axis of the common holder is pivoted relative to the axis ofrotation.
 10. The method according to claim 9, wherein the first andsecond set of forming rollers are moved relative to each other duringsaid working.
 11. The method according to claim 9, wherein the edge ofthe workpiece is supported at least during part of the operation. 12.The method according to claim 1, wherein the workpiece comprises a metalcylinder or plate.
 13. The method of claim 1 wherein the common holderis radially adjusted during the working of the workpiece.
 14. A formingmachine suitable for manufacturing products which forming machinecomprises at least a clamping device for clamping down a workpiece, afirst set of forming rollers, which can be placed into contact with theworkpiece while being worked, means for rotating the workpiece and thefirst set of forming rollers about an axis of rotation relative to eachother, and means for moving the workpiece and/or the first set offorming rollers in a direction along said axis of rotation, and at leasta second set of forming rollers disposed behind said first set offorming rollers, which can be placed into contact with the workpiece andwherein two or more forming rollers associated with different sets offorming rollers are mounted on a common holder such that perimeters ofadjacent forming rollers at least partially overlap and wherein thefirst set of forming rollers are spaced apart from the second set ofrollers such that the first and second sets of rollers do not contacteach other and said holder is pivotally mounted in or on the formingmachine in such manner as to be capable tilting toward or away from saidaxis of rotation such that a tilting axis of the holder crosses saidaxis of rotation during the forming process of the workpiece.
 15. Theforming machine according to claim 14, comprising at least a third setof forming rollers disposed behind said second set of forming rollers.16. The forming machine according to claim 14, wherein the first andsecond sets of forming rollers each comprise two or more formingrollers, between which the workpiece can be retained.
 17. The formingmachine according to claim 14, wherein the first and second sets offorming rollers can be moved relative to each other during the working.18. The forming machine according to claim 14, comprising a mandrel orbush to be placed in or around, respectively, an unworked part of theworkpiece, and by means of which a tensile force can be exerted on theworkpiece.
 19. The machine of claim 14 wherein the common holder isradially adjusted during the working of the workpiece.
 20. A formingmachine suitable for manufacturing products which forming machinecomprises at least a clamping device for clamping down a workpiece, aplurality of forming rollers mounted on a first common holder, which canbe placed into contact with the workpiece while being worked, means forrotating the workpiece and the plurality of forming rollers about anaxis of rotation relative to each other, and means for moving theworkpiece and/or the plurality of forming rollers in a direction alongsaid axis of rotation, wherein the first common holder moves radiallywith respect to an axis of rotation of the workpiece and also movespivotally with respect to the axis of rotation of the workpiece and atleast one or more forming rollers mounted on a second holder and spacedfrom the first common holder wherein the second holder moves radiallywith respect to the axis of ration of the workpiece, wherein at leastone of the plurality of forming rollers mounted on the first commonholder and the at least one forming roller mounted on the second holderengages the workpiece and wherein the first and second holders aremounted in or on the forming machine in such manner such that the firstcommon holder is capable of rotation about an axis which crosses saidaxis of rotation during the formation of the workpiece.
 21. The formingmachine of claim 20 and wherein each of the forming rollers are radiallypositionable independent of the other rollers.
 22. The machine of claim20 wherein the common holder is radially adjusted during the working ofthe workpiece.
 23. A method for manufacturing a product having aconstant diameter or various diameters from a workpiece, in which theworkpiece is clamped down in a clamping device, the workpiece and afirst set of forming rollers are rotated about an axis of rotationrelative to each other, wherein the rollers of the first set take up afirst same axial position with respect to the work piece, wherein theworkpiece is deformed by means of said forming rollers by placing theforming rollers into contact with the workpiece and moving the workpieceand/or the forming rollers in a direction along said axis of rotation,wherein at least a second set of forming rollers positioned at a secondaxial position with respect to the work piece is placed into contactwith the workpiece at a position behind the first set of formingrollers, the workpiece also being deformed by means of said second setof forming rollers and wherein two or more forming rollers, each beingof a different set and taking up a different axial position with respectto the work piece, are mounted on a common holder and said holder isrotated about an axis which crosses said axis of rotation duringoperation such that an outer surface of the workpiece is contacted bythe first and second set of rollers.
 24. The method of claim 23 whereinthe common holder is radially adjusted during the working of theworkpiece.